Hello.
I have a relay card with 8 relays http://www.electrokit.com/relakort-x-8.46147 Link to documentation http://www.electrokit.com/productFile/download/515
The relay card is controlled with ttl inputs (2v - 5v)
So i was thinking that maybe its possible to use the internal 5v from the K8055 and the digital output and connect this to the Relay card. But i need some help how i should connect this.
Maybe someone could point me in the right direction.
Your idea can work, but it would invert the logic. If you use pull up resistors from the USB +5V supply to the 8 inputs of the relay card, and the 8 digital outputs of the K8055 to pull them low, the relays would be ON when the corresponding K8055 output is OFF.
Let me suggest a different path, that interestingly needs no extra components at all.
Note that the IC U1 on the relay card is the very same ULN2803, that is used for the digital outputs on the K8055. The one on the K8055 is driven by the TTL signals coming from the PIC.
Remove the IC U1 from the relay card. Connect the K8055’s O1…O8 to the IC U1 socket pins 18…11 (labeled OP1…OP8 in the schematics). Connect +V and GND of connector CN10 to the K8055’s CLAMP and GND. You still need a 12V power source connected to CN10 because that is what is actually driving the relay coils. You will need that one no matter what, because the ULN2803 is just an open collector Darlington Transistor array.
Hope this helps.
Regards,
Jan
Thanks.
That sounds like a great solution. I will test this.
You are very welcome.
Regards,
Jan